Nowadays, electronic devices serving as information terminals, for example, disk array devices that each includes a plurality of hard disk drives mounted therein and servers are vertically stacked in a system rack in use. Internal circuits of the vertically stacked electronic devices in the system rack are, in most cases, electrically connected to each other. When the electronic devices are connected to each other, connectors mounted on the front or rear surfaces of enclosures of the electronic devices are usually connected to each other using cables (refer to Japanese Laid-open Patent Publication No. 8-221154). Alternatively, a female connector and a male connector are respectively provided at positions opposing each other on an upper surface and on an lower surface of the electronic device so as to connect the female connector to the male connector when the electronic device and the other electronic device are stacked one on top of the other (refer to Japanese Laid-open Patent Publication No. 8-221154 and Japanese Laid-open Patent Publication No. 6-195153).
When cables are used to connect the connectors mounted in the front or rear surfaces of the enclosures of the electronic devices to each other in order to connect the electronic devices vertically stacked in the system rack, the length of each connection cable is set to a length longer than the minimum connection length. The connection cable needs to have a degree of extra length for allowing insertion or removal of the connectors when the bending radius of the cable and properties of the cable in wiring are considered.
In a structure in which female and male connectors are respectively provided at positions opposing each other on the upper and lower surfaces of the enclosure of the electronic devices so as to connect the female connector to the male connector when the electronic devices are stacked one on top of the other, the male connector protrudes from the uppermost upper surface or the lowermost lower surface. For this reason, the enclosure of the uppermost or lowermost electronic device has a structure different from that of the intermediate electronic device so as to prevent the male connector from protruding from the uppermost upper surface or the lowermost lower surface.
When internal circuits of vertically stacked electronic devices are connected to each other with cables, the number of the cables increases as the number of the stacked electronic devices increases, thereby increasing transmission distances of signals between the electronic devices. As a result, phenomena disadvantageous for performance such as voltage reduction and noise contamination occur. In addition, since components used in the electronic devices are increasingly densely mounted, the electronic devices need much cooling air flowing into the enclosures. However, when connection cables are routed on the front or rear surfaces of the enclosures, there is a problem in that the cables block the flow of cooling air, thereby decreasing cooling capacity.
When circuits of vertically stacked electronic devices are directly connected to each other using female and male connectors, the structure of the enclosure needs be changed so as to prevent the male connector from protruding from the upper surface of the uppermost enclosure or the lower surface of the lowermost enclosure. Furthermore, the circuits of the vertically stacked electronic devices are all connected to each other using the connectors. This does not allow the circuitry in the enclosure disposed at an intermediate location to be unconnected.